1. Field of the Invention
This invention lies in the field of quality controls for assays of analytes in biological fluids.
2. Description of the Prior Art
Quality control materials are routinely used in clinical diagnostics laboratories to monitor the precision and accuracy of assay equipment, materials, and procedures with which assays are performed either manually or by automation. Examples of commonly assayed analytes are drugs, hormones, enzymes, and antibodies; others will be readily apparent to the experienced biochemist. Controls for assays of human samples are typically prepared by adding a known quantity of the target analyte to a processed human base matrix such as human serum or human urine since matrices such as these ensure that the controls are as sensitive to all anticipated analytical variances as the actual patient samples. Many of these controls are prepared in solid form by lyophilization of the fully constituted liquid, leaving the user with the simple task of rehydrating the solid by dissolving it in water.
Commercially available controls, whether for a single analyte or for multiple analytes, are commonly offered in bi-level or tri-level combinations to provide levels that are above, near, and below the medical decision point for each assay. Many of these controls are directed to groups of related analytes, such as tumor markers, for example, or analytes measured by one type of detection technology, such as routine chemistry analytes measured by photometry or urinalysis analytes measured by reflectance photometry using dry chemistry strips. In general, the controls are designed, developed, and optimized for use in certain common test methods and technologies and are often not useful for purposes that extend beyond these common uses, particularly purposes that entail different levels of concentration, different assay methodologies, and different reasons for conducting the assays.
Clinical diagnostic assays can differ in such factors as precision, accuracy, limits of quantitation, limits of detection, linearity, and reportable range, due to differences in assay architecture, detection technology, and source of supply of the assay. Assays for certain analytes lack standardization in such features as medical decision points, for example, and therefore the controls that are supplied with these assays are not fully interchangeable nor are they useful for quality control at detection levels that are outside the ranges spanned by the controls. Currently available assays for Troponin I, for example, are designed for decision points that vary from one supplier to the next by a factor as high as 4. Patient populations differ as well, and in some cases the decision points differ so much between populations that controls designed for one population are not suitable for another.